The trend of the LED toward higher output and higher efficiency has been adding to the range of applications to be found for the LED. In addition to the conventional use in colored indicators and outdoor large displays, the LED has been rapidly increasing the volume of use in the backlight source for a display of the mobile phone, the headlight, and the light source for illumination. For the sake of answering these needs for the LED, it has become necessary for the LED to attain further enhancement in output and efficiency.
The green to ultraviolet light-emitting diode 2 formed of a nitride compound semiconductor is generally known in two kinds, the type having the nitride compound semiconductor stacked on the front face of a sapphire substrate, forming a p-electrode and an n-electrode on the front side of the nitride compound semiconductor and connecting the electrodes with two Au wires 1 to a package lead 5 (refer to FIG. 1) and the type having the nitride compound semiconductor stacked on an SiC substrate, forming an n-electrode on the back side of the substrate and a p-electrode on the front side of the nitride compound semiconductor and connecting the back side of the substrate via one Au wire to the package lead. In the diagram, reference numeral 3 denotes a sealing resin and numeral 4 a molded body. In these configurations, the Au wires constitute such parts as cause loss of the light-emitting output because they absorb the light in the green to ultraviolet regions. As regards the problem of the absorption posed by the Au wire, a method which abates the loss by causing the resin mold wholly enclosing a light-emitting element to contain a fluorescent material capable of transforming the emitted light into a visible light having a longer wavelength than the wavelength of the emitted light, thereby enabling the light prior to impinging on the Au wire to be transformed into the light of the longer wavelength at which the Au wire exhibits a low light absorption factor has been disclosed (refer to Japanese Patent No. 2900928).
As a technique for coating a fine metallic wire for use in wire bonding, the coating of a gold wire with tin for the purpose of decreasing the cost of production, for example, has been disclosed (refer to JP-A SHO 62-227592). With the object of reconciling the reduction of cost and the enhancement of adhesive property, a bonding wire for use in connecting a semiconductor element, which wire is formed of a fine metallic wire of copper, aluminum or gold and has the surface of the fine wire coated with a metal having higher purity than the metal of the wire but equaling in kind thereto has been disclosed (refer to JP-A SHO 62-287633). These methods, however, are incapable of heightening the light reflection coefficient in the portion of the bonding wire.
This invention is aimed at providing a means for coping with the loss of absorption of light caused by a bonding wire of Au or Cu, i.e. a metal inducing absorption of light in the green to ultraviolet regions, and as well providing a light-emitting device which exhibits high output and high efficiency in consequence of the abatement of the loss. This invention is further aimed at promoting the addition to the output and efficiency of not only the green to ultraviolet monochromatic short-wavelength light-emitting element but also the white LED or any colored LED which has incorporated therein a wavelength-converting substance utilizing a green to ultraviolet short-wavelength light-emitting element as an excitation source.
This invention consists in accomplishing the objects mentioned above by coating the surface of an Au wire or a Cu wire serving as a bonding wire with a substance capable of heightening the coefficient of reflection of the light emitted from the LED and consequently imparting an enhanced light reflection coefficient to the bonding wire.